OBJECTIVE LIFE SCIENCE
EVOLUTION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Common fossils from a distinct time period; useful in defining geologic time periods.
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Rare fossils from a distinct time period; useful in defining geologic time periods.
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Common fossils from an unknown time period
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Rare fossils from an unknown time period.
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Detailed explanation-1: -Index fossils are the basis for defining boundaries in the geologic time scale and for the correlation of strata. In marine strata, index fossils that are commonly used include the single-celled Protista with hard body parts and larger forms such as ammonoids.
Detailed explanation-2: -Index fossils are used to define geological periods. These fossils can be defined as “commonly found, widely distributed fossils that are limited in time span.” If one finds an index fossil in a given layer, then one has bounds on the age of the layer.
Detailed explanation-3: -Ammonites, trilobites, and graptolites are often used as index fossils, as are various microfossils, or fossils of microscopic organisms. Fossils of animals that drifted in the upper layers of the ocean are particularly useful as index fossils, as they may be distributed all over the world.
Detailed explanation-4: -Some of the most common index fossils are ammonites, trilobites, and graptolites. Index fossils are vital components in relative dating-a method of determining the order of geological events without knowing their numerical dates.
Detailed explanation-5: -Fossils are used to determine the ages of rock layers. Index fossils are the most useful for this.